METHODS OF MEASURING BLOOD FLOW 



1291 



4 - 



3 - 



2 



fig. i. Typical arterial (A) and internal jugular (V) curves 

 of N 2 concentration during a 10-min period of inhalation of 

 [5% N l .O. [From Kety & Schmidt (22).] 



and one venous, during the measuring period of 10 

 min. The advantages of this modification are seen 

 in the fact that a) only one person is needed for taking 

 the samples, b) less blood is taken from the patient, 

 and c) the number of gas analyses is reduced from 

 ten to three (25). The modified method yields results 

 identical with those obtained with the original 

 method. However, Kety (24) prefers his primary pro- 

 cedure of intermittent sampling since he believes that 

 the course of arterial and venous time concentration 

 curves allows an estimation of the volume of blood 

 from extracranial vessels which has been intermixed 

 with cerebral blood flow. This point is of general im- 

 portance and will be briefly discussed here. The main 

 premise is that representative mixed venous blood 

 of the brain is obtained for measurement of gas con- 

 centrations. It is not necessary for the total blood 

 flow of the organ to pass through one vein. However, 

 it is required that the concentration of test substance 

 be equal in all veins. Samplings from the bulbus 

 cranialis of the internal jugular vein have proved to 

 be fairly free of extracranial blood. Shenkin et al. (40) 

 estimate a maximal admixture of 2 to 3 per cent. For 

 proper use of the partition coefficient of nitrous oxide 

 in blood and tissue — its value for cerebral tissue is 

 about one — it is important that concentration equilib- 

 rium between tissue and blood has been reached. 

 Even small differences between arterial and venous 

 concentration lead to errors, as Sapirstein & Ogden 

 (37) have shown. This fact would seem to make the 

 original intermittent sampling technique the method 



of choice. Simultaneous measurements of cerebral 

 blood flow in monkeys by the nitrous oxide method 

 and by bubble flowmeter show good agreement (22). 



MEASUREMENT OF CORONARY BLOOD FLOW. Soon after 



the introduction of the nitrous oxide method for the 

 determination of cerebral blood flow, the method was 

 used to measure coronary blood flow (6, 7, 12). The 

 blood of the coronary sinus is representative of the 

 left ventricular coronary flow, and since the improve- 

 ment of catheterization technique has made it pos- 

 sible to sample blood from the coronary sinus, the 

 nitrous oxide method can be applied successfully in 

 man (4). In coronary blood flow experiments on dogs, 

 Gregg and co-workers (14) found good agreement 

 between values obtained by use of the rotameter and 

 the nitrous oxide method. A series of investigations 

 has been undertaken using the desaturation course 

 of nitrous oxide. The results were similar to those 

 obtained by the method of saturation [Goodale & 

 Hakel (1 1 ) and Bargeron et al. (2)]. 



Other Test Substances 



Radioactive krypton 85 has been proposed by 

 Lassen & Munck (26, 29) for use in the determination 

 of cerebral blood flow. The procedure is very similar 

 to that of the nitrous oxide method. The application 

 of krypton 85, although it allows greater accuracy, 

 has the disadvantage of requiring special instrumenta- 

 tion and the risk to the patient of radiation exposure. 

 Munck & Lassen have recommended that internal 

 jugular blood should be sampled bilaterally because 

 concentration of the test substance may differ in the 

 two veins. Blood flow is then calculated twice and 

 the mean is taken. Since gaseous test substances re- 

 quire special care in sampling and storing of blood, 

 and since the analyses are time consuming and diffi- 

 cult under conditions of gaseous anesthesia, Huckabee 

 (17) proposed the use of 4-aminoantipyrine. This is 

 a nonvolatile, biologically inert substance, which 

 diffuses rapidly from blood into tissue fluid, and is 

 relatively easy to measure. [See also (14), (19), (18).] 



TEST-SUBSTANCE DILUTION METHODS 



These also employ the Fick principle. Blood flow 

 through an organ is determined from the ratio of the 

 amount of injected test substance to its concentration 

 in the effluent blood. In case there is, for any reason, 

 some of the indicator substance in the blood at the 



